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Fuel Tanks

Fuel is stored in the wings and the trimmable horizontal stabiliser. The wings have inner and outer tanks. The inner tanks contain collector cells that are maintained full at about 1,000kg of fuel to keep the pumps pressurised and give -ve 'g' protection. There are 2 main pumps and a standby pump in each inner tank, the standby pump being outside of the collector cells. Any 1 pump is sufficient to supply the engines. The split valve normally remains open although may be closed if tank damage is suspected.

_{Figure: Inner fuel tank}

Two outer tank transfer valves (OUTR TK XFR) allow fuel to transfer from the outer to the inner tanks. Two engine low pressure valves are installed to cut off fuel from the engines. Another low pressure valve cuts off fuel to the APU. There is a crossfeed valve to isolate or connect the left and right wing tanks, which fails open in an electrical emergency.

A trim tank isolation valve and a trim tank inlet valve (represented by 1 valve symbol on FUEL page) allow fuel to transfer betwen the trim tank and the inner tanks.

The LP fuel valves are controlled by the engine master switches and the engine fire pushbuttons.

External components

Magnetic fuel level indicators and water drain points are located in each fuel tank. Refuel couplings are installed under both left and right wings. When both are used, refuelling time is approximately 33 mins. Surge tanks are connected to the outer tank in each wing tip and on the right side of the trim tank, and protect against overpressure and thermal expansion.

Fuel feed

Fuel is always fed to the engines from the inner tanks. During takeoff and initial climb, the engines are fed from their collector cell. Note that the engines also suction feed if the fuel pumps are switched off.

Fuel pumps

In an electrical emergency, pumps L2 and R2 remain.

Fuel transfer

Trim Tank ↔ Inner Tanks

The FCMC calculates CG during during cruise and uses actual weight to optimise the CG position by transferring fuel to or from the trim tank. With actual CG forward of target CG above FL255, an aft transfer occurs and stops when CG is target CG -0.5% (ie. 0.5% forward of target CG). The transfer stops on the lightest side if the inner tanks are out of balance by more than 500 kg, until balance is recovered. There is no manual aft transfer. For an aft transfer to occur, the inner tanks' fuel quantity must be > 6,250 kg.

For a forward transfer, if the inner tanks are 500 kg out of balance, the transfer is stopped on the heaviest side until balance is recovered. A forward transfer also occurs when inner tank contents reach 4,000 kg, and fuel is maintained in the inner tanks between 4,000 kg and 5,000 kg.

A continuous forward transfer also occurs descending through FL245, or when time to destination is less than 35 min (75 min when the trim tank forward transfer pump has failed due to the longer time required by a gravity transfer). It stops automatically when the landing gear or slats are extended. Balance is maintained within 2,000 kg.

See also Trim Tank Transfers.

Outer Tanks → Inner Tanks

When inner tank quantity is below 3,500 kg with the trim tank empty, the outer tank transfer valves open to keep inner tank quantity between 3,500 kg and 4,000 kg. The transfer is done by gravity. If the transfer is done manually, it continues until the outer tanks are empty.

Outer tank transfer valves close automatically when outer tanks are empty for 5 min. During a manual transfer, aft transfer is inhibited.

Quantity

_{Table: Fuel quantity (exact quantities depend on aircraft mod)}

Failures

See also

Trim Tank Transfers

A340 Fuel Tanks

Categories: Airbus A330 | Fuel System